1. Field of the Disclosure
The invention relates to superconductive articles and methods of making superconducting articles, more specifically to textured films formed by ion beam assisted deposition.
2. Description of the Related Art
Superconductor materials have long been known and understood by the technical community. Low-temperature (low-Tc) superconductors exhibiting superconductive properties at temperatures requiring use of liquid helium (4.2 K), have been known since about 1911. However, it was not until somewhat recently that oxide-based high-temperature (high-Tc) superconductors have been discovered. Around 1986, a first high-temperature superconductor (HTS), having superconductive properties at a temperature above that of liquid nitrogen (77 K) was discovered, namely YBa2Cu3O7−x (YBCO), followed by development of additional materials over the past 15 years including Bi2Sr2Ca2Cu3O10+y (BSCCO), and others. The development of high-Tc superconductors has created the potential of economically feasible development of superconductor components incorporating such materials, due partly to the cost of operating such superconductors with liquid nitrogen rather than the comparatively more expensive cryogenic infrastructure based on liquid helium.
Of the myriad of potential applications, the industry has sought to develop use of such materials in the power industry, including applications for power generation, transmission, distribution, and storage. In this regard, it is estimated that the native resistance of copper-based commercial power components is responsible for billions of dollars per year in losses of electricity, and accordingly, the power industry stands to gain based upon utilization of high-temperature superconductors in power components such as transmission and distribution power cables, generators, transformers, and fault current interrupters. In addition, other benefits of high-temperature superconductors in the power industry include a factor of 3-10 increase of power-handling capacity, significant reduction in the size (i.e., footprint) of electric power equipment, reduced environmental impact, greater safety, and increased capacity over conventional technology. While such potential benefits of high-temperature superconductors remain quite compelling, numerous technical challenges continue to exist in the production and commercialization of high-temperature superconductors on a large scale.
Among the challenges associated with the commercialization of high-temperature superconductors, many exist around the fabrication of a superconducting tape that can be utilized for formation of various power components. A first generation of superconducting tape includes use of the above-mentioned BSCCO high-temperature superconductor. This material is generally provided in the form of discrete filaments, which are embedded in a matrix of noble metal, typically silver. Although such conductors may be made in extended lengths needed for implementation into the power industry (such as on the order of kilometers), due to materials and manufacturing costs, such tapes do not represent a commercially feasible product.
Accordingly, a great deal of interest has been generated in the so-called second-generation HTS tapes that have superior commercial viability. These tapes typically rely on a layered structure, generally including a flexible substrate that provides mechanical support, at least one buffer layer overlying the substrate, the buffer layer optionally containing multiple films, an HTS layer overlying the buffer film, and an electrical stabilizer layer overlying the superconductor layer, typically formed of at least a noble metal. However, to date, numerous engineering and manufacturing challenges remain prior to full commercialization of such second generation-tapes.
One of the more difficult challenges in creating commercially viable second generation-tapes has been the formation of a biaxially textured HTS layer. In the past, a biaxially textured HTS layer has been achieved by epitaxially growing the HTS layer on top of at least one biaxially textured buffer film. Typically, the biaxially textured buffer films have been formed using a process known as ion beam assisted deposition, or IBAD in order to create the proper crystalline template for epitaxial growth of a suitable biaxially textured HTS layer. The initial films in the buffer layer initialize the templating effect towards forming a suitable biaxially textured buffer film and HTS layer. However, such methods have proven particularly demanding because they require deposition of layers having a precise crystal structure and texture to ensure the proper epitaxial growth of a suitable HTS layer.
While the formation of an effective biaxially textured buffer film has improved with the advent of the IBAD process, given the rigorous requirements in growing a particular crystal structure with particular texture, the formation of the buffer stack is still a relatively slow and expensive process. Such requirements, while important, impose a significant impediment to the large-scale production of superconducting tapes, since it would affect the ability to produce a low-cost HTS tape.
Accordingly, there is a need in the art for improved methods of forming superconducting components. In particular, there is a need in the art for improved processing techniques for creating constituent layers of a superconducting article having precise crystal structure and texturing, and for producing commercially viable HTS articles and devices.